Research has provided support for the efficacy of family interventions for adolescent substance use disorders (SUD), conduct/delinquent behaviors, and HIV risk behaviors. Advances in successfully treating such difficulties have resulted in an increased emphasis to redirect resources to transport evidence-based treatments (EBTs) into real-world community settings. The urgency of this call is reflected in increasing efforts by insurance companies, community agencies, and public advocates to bring EBTs to larger segments of our society. Efforts to transport efficacious interventions into practice settings, however, have met with limited success. Moreover, the successful transport of EBTs and the subsequent achievement of positive outcomes in effectiveness trials are intrinsically linked and the need for systematic investigation to understand the parameters for successful implementation in community settings is widely recognized. The proposed study is intended to address a critical gap in research on the treatment of adolescent SUD, conduct/delinquent, and HIV risk behaviors by examining the ongoing supervision of therapists in community settings. The research proposed represents a Stage III effectiveness study which will evaluate two distinct approaches to therapist supervision in the implementation of Functional Family Therapy (FFT), an EBT for adolescent substance abuse, conduct/delinquent behaviors, and HIV risk behaviors. The study is designed to capitalize on the extensive FFT dissemination infrastructure, that includes a cadre of fully trained FFT therapists within sites that have already adopted and implemented FFT, to examine how two distinct supervision strategies affect therapist competent adherence to the intervention model and, ultimately, clinical outcomes in real world implementation. We will compare the effects of an observation-based supervision (BOOST) to the standard supervision as usual (SAU) approach currently used by FFT LLC on therapist competence and adolescent behavioral outcomes. The study will be implemented with 16 FFT teams affiliated with the California Institute of Mental Health, the coordinating center for stakeholders implementing FFT in the State of California. Participants will include 3 therapists from 16 FFT teams (n=48) and 6 adolescents/families per therapist (n=288). Therapist teams will be randomly assigned to BOOST or SAU. The aims of the study are: (1) To examine differences between BOOST and SAU in improving adolescent substance use (Aim 1a), conduct/delinquent behaviors (Aim 1b), and HIV risk behaviors (Aim 1c). (2) To examine differences between BOOST and SAU in improving engagement and retention in treatment. (3) To examine differences between BOOST and SAU in the rates of therapist competence (Aim 3a) and improvements in family functioning (Aim 3b). (4) To explore whether therapist competence mediates (Aim 4a) the association between supervision condition and treatment outcomes, improvements in family functioning, and greater rates of engagement and retention in treatment. We also will explore whether improvements in family functioning (Aim 4b) mediates the link between supervision condition and treatment outcomes.